Amorphous metallic alloys substantially lack any long range atomic order and are characterized by X-ray diffraction patterns consisting of diffuse (broad) intensity maxima, quantitatively similar to the diffraction patterns observed for liquids or inorganic oxide glasses. However, upon heating to a sufficiently high temperature, they begin to crystallize with evolution of the heat of crystallization; correspondingly, the X-ray diffraction pattern thereby begins to change from that observed for amorphous to that observed for crystalline materials. Consequently, metallic alloys in the amorphous form are in a metastable state. This metastable state of the alloy offers significant advantages over the crystalline form of the alloy, particularly with respect to the mechanical and magnetic properties of the alloy.
Understanding which alloys can be produced economically and in large quantities in the amorphous form and the properties of alloys in the amorphous form has been the subject of considerable research over the past 20 years. The most well-known disclosure directed to the issue--What alloys can be more easily produced in the amorphous form?--is U.S. Pat. No. Re 32,925, to H. S. Chen and D. E. Polk, assigned to Allied-Signal Inc. Disclosed therein is a class of amorphous metallic alloys having the formula M.sub.a Y.sub.b Z.sub.c, where M is a metal consisting essentially of a metal selected from the group of iron, nickel, cobalt, chromium, and vanadium, Y is at least one element selected from the group of phosphorus, boron and carbon, Z is at least one element from the group consisting of aluminum, antimony, beryllium, germanium, indium, tin and silicon, "a" ranges from about 60 to 90 atom percent, "b" ranges from about 10 to 30 atom percent and "c" ranges from about 0.1 to 15 atom percent. Today, the vast majority of commercially available amorphous metallic alloys are within the scope of the above-recited formula.
With continuing research and development in the area of amorphous metallic alloys, it has become apparent that certain alloys and alloy systems possess magnetic and physical properties which enhance their utility in certain applications of worldwide importance, particularly in electrical applications as core materials for distribution and power transformers, generators and electric motors.
Early research and development in the area of amorphous metallic alloys identified a binary alloy, Fe.sub.80 B.sub.20, as a candidate alloy for use in the manufacture of magnetic cores employed in transformers, particularly distribution transformers, and generators because the alloy exhibited a high saturation magnetization value (about 178 emu/g). It is known, however, that Fe.sub.80 B.sub.20 is difficult to cast into amorphous form. Moreover, it tends to be thermally unstable because of a low crystallization temperature and is difficult to produce in ductile strip form. Further, it has been determined that its core loss and exciting power requirements are only minimally acceptable. Thus, alloys of improved castability and stability, and improved magnetic properties, had to be developed to enable the practical use of amorphous metallic alloys in the manufacture of magnetic cores, especially magnetic cores for distribution transformers.
Ternary alloys of Fe--B--Si were identified as superior to Fe.sub.80 B.sub.20 for use in such applications by Luborsky et al. in U.S. Pat. Nos. 4,217,135 and 4,300,950. These patents disclose a class of alloys represented generally by the formula Fe.sub.80-84 B.sub.12-19 Si.sub.18 subject, however, to the provisos that the alloys must exhibit a saturation magnetization value of at least about 174 emu/g (a value presently recognized as the preferred value) at 30.degree. C., a coercivity less than about 0.03 Oersteds and a crystallization temperature of at least about 320.degree. C.
Subsequent to Luborsky et al., it was disclosed in application Ser. No. 220,602, to Freilich et al., assigned to Allied-Signal Inc., that a class of Fe--B--Si alloys represented by the formula Fe.sub..apprxeq.75-78.5 B.sub.26 11.apprxeq.21 Si.sub..apprxeq.4.apprxeq.10.5 exhibited high crystallization temperature combined with low core loss and low exciting power requirements at conditions approximating the ordinary operating conditions of magnetic cores in distribution transformers (i.e., 60 Hz, 1.4 T at 100.degree. C.), while maintaining acceptably high saturation magnetization values.
U.S. patent application Ser. No. 235,064 discloses a class of Fe--B--Si alloys represented by the formula Fe.sub.77-80 B.sub.12-16 Si.sub.5-10 and discloses that these alloys exhibit low core loss and low coercivity at room temperature after aging, and have high saturation magnetization values.
More recently, U.S. Pat. No. 4,437,907 disclosed a class of Fe--B--Si alloys represented by the formula Fe.sub.74-80 B.sub.6-13 Si.sub.8-19, optionally containing up to 3.5 atom percent carbon, which alloys exhibit after aging a high degree of retention of the original magnetic flux density of the alloy (measured at 1 Oe and room temperature).
In addition, U.S. application Ser. No. 883,870, filed Jul. 14, 1986, to Nathasingh et al., assigned to Allied-Signal Inc., discloses a class of alloys useful for manufacture of magnetic cores for distribution transformers which are represented by the formula Fe.sub.79.4-79.8 B.sub.12-14 Si.sub.6-8, which alloys exhibit unexpectedly low core loss and exciting power requirements both before and after aging in combination with an acceptably high saturation magnetization value.
It is readily apparent from the above discussion that researchers focused on different properties as being critical to the determination of which alloys would be best suited for the manufacture of magnetic cores for distribution and power transformers, but none recognized the combination of properties necessary for clearly superior results in all aspects of the production and operation of magnetic cores and, consequently, a variety of different alloys were discovered, each focusing on only part of the total combination. More specifically, conspicuously absent from the above recited disclosures is an appreciation for a class of alloys wherein the alloys exhibit a high crystallization temperature and a high saturation magnetization value, in combination with low core loss and low exciting power requirements after having been annealed over a wide range of annealing temperatures and times and, in addition, retain their ductility over a range of annealing conditions. Alloys which exhibit this combination of features would find overwhelming acceptance in the transformer manufacturing industry because they would possess the magnetic characteristics essential to improved operation of the transformer and more readily accommodate variations in the equipment, processes and handling techniques employed by different transformer core manufacturers.